The goal of this project is to elucidate the anatomical, electrophysiological and neurochemical properties of neurons in mammalian retinas and to infer the interactions and interconnections which comprise retinal neural circuits, and so to obtain further insights into retinal functions in normal and diseased states. Color vision in cats is controversial, nonetheless studies of the spectral sensitivities of cat horizontal cells have revealed three cone types: a blue type with a peak sensitivity at 440 nm, a green type peaking at approximately 520 nm, and a red type maximally sensitive at 560 nm. Interactions among the cones have also been observed with suggestions of blue inhibiting green, and green inhibiting red. Some cat horizontal cells are shown to be spectrally tetrachromatic with input from these three cone types as well as rods. The contributions of the two shorter wavelength peaking cones become especially prominent on dim red backgrounds. Although different horizontal cells show partial selectivity for cones, this appears unrelated to the classical anatomical divisions between the axonless A-type cells and the axon bearing B-type cells. Only the red cones were found to be dynamically rapid enough to follow 10 Hz flicker, leading to a convenient test to separate red from blue and green cone signals. Surprisingly, one rod-connected horizontal cell axon terminal, although exhibiting rod-dominated responses in the dark adapted state, showed a dominant blue cone selectivity with red backgrounds. Results suggest that interreceptor contacts between cones may function to intermix signals from different chromatic types of cone at the receptor level.